Apple tree named `M9-RN8`

ABSTRACT

This invention relates to a new and distinct apple tree rootstock clone which is useful as a size-controlling rootstock. The new clone originated as a mutation of Malling 9 (M9), an unpatented dwarfing apple rootstock, Standard growing apple cultivars propagated on this new rootstock are approximately 70 % of the size of like apple trees growing on apple seedling rootstocks. In the stoolbed the clone produces few lateral limbs, large round to oval leaves with broadly acute tips and possesses a pronounced, profuse blooming characteristic. The clone produces a larger number of rooted plants in the stoolbed.

BACKGROUND AND SUMMARY OF THE INVENTION

The subject clone is a sport of Malling 9 MM9), an unpatented apple rootstock clone. The original plant was selected as a mutation in 1967 from a large stoolbed of M9 plants. The stoolbed had been planted in 1960 and was growing in the Rene Nicolai nursery, Linderstroot, 22-B-3820 Alken, Belgium. The original source of the bed was the East Malling Research Station in England. The clone was one of a group of clones that were selected by Mr. Nicolai and other rootstock specialists for their differences in lateral branching, leaf development and shape, leaf color, thickness of the shoots, rooting ability in the stoolbed, bloom characteristics and other noticed differences from the mother stoolbed plants.

Following its selection, the clone was assigned a number (RN8) and was propagated for further testing and evaluation.

Since all original M9 rootstocks have been found to be virus infected, RN8 stocks were subsequently heat-treated by application of dry heat in order to obtain virus-free specimens. After heat treatment and subsequent virus testing, the new rootstock clone was again exposed to multiplication techniques (stooling) followed by continued testing and evaluation.

Virus-free RN8 progeny plants were expanded into small stoolbed plantings which were planted separately rately in order to examine the new rootstocks's individual characteristics in small semi-commercial stoolbed sites.

These small experimental stoolbeds of RN8 were established for such further evaluations as follows:

1. A site at Deveaux, Belgium was planted in the spring of 1974 with 555 plants of the subject clone.

2. A site at Bordeaux, France was planted in 1977 with 200 plants of the subject clone.

3. A site at Wissenhoeve, Belgium was planted in the spring of 1980 with 1,176 plants of the subject clone.

4. A site near St. Truiden, Belgium was planted in the spring of 1982 wtih 100 plants of the suject clone.

5. A site at Henkaenrts, Belgium was planted in the spring of 1986 with 4,600 plants of the subject clone.

6. A site at Ephrata, was planted in the spring of 1990 with 2,000 plants of the subject clone.

Clone RN8 was subsequently finally selected as a rootstock clone that continues to possess growth and rooting characteristics that are distinctly different from its M9 parent.

It distinguished itself in these beds from its M9 parent in the following ways:

1. The subject clone produces fewer lateral limbs (feathers) than its M9 parent. At the Bordeaux test site in France and at the Ephrata, Wash. site, feathers produced were about one half the number produced on its M9 parent (FIGS. 1 and 2; Tables 1 and 2). RN8 grows less robustly in the stoolbed and exhibits a shorter, stockier growth characteristic when compared to its M9 parent (FIG. 4, M9; and FIG. 5, RN8). Nodes are spaced closer together on shoots and average stem circumference is significantly more than the average stem Circumference of M9 (Table 2). The average length of feathers on RN8 was slightly less than the average length of feathers on its M9 parent (Table 2).

                  TABLE 1     ______________________________________     Percent of Layer Plants with Side Limbs (Feathers)     (Test Stooling Beds at Bordeaux, France)     Rootstock Year     Clone     79/80    80/81  81/82  82/83                                           Average     ______________________________________     M9        13       8      25     0    11.5     (virus-free)     RN8       8        6      13     0    6.8     RN19      41       32     44     19   34.0     RN29      39       22     35     15   27.8     ______________________________________

                  TABLE 2     ______________________________________     Growth Characteristics     (Test Stooling Beds at Ephrata, Washington)            Length  Number   Number                                   Length                                         Number Circum-            of      of       of    of    of     ference     Rootstock            Shoot   Nodes/   Spurs/                                   Spur  Leaves/                                                of Stem     Clone  (cm)    Shoot    Shoot (cm)  Shoots (cm)     ______________________________________     M9     66.80*  39.20    3.00  1.50  53.00  3.24     RN8    62.10   42.10    1.80  1.20  57.20  3.80     RN19   78.20   41.00    18.60 8.60  88.30  3.51     RN29   86.20   45.60    21.40 10.30 100.00 3.54     ______________________________________      *All numbers shown are the average of 100 plants selected at random.

2. Leaves of the subject clone are larger and more rounded in shape and leaf margins are more sinuate than those of M9. Leaves of RN8 are round to oval in shape with broadly acute tips. Theis leaf characteristic is very pronounced in the older leaves (FIG. 3; Table 3).

                  TABLE 3     ______________________________________     Leaf Size and Respetive Petiole     Length of Respective Rootstock     (Test Stooling Beds at Bordeaux, France)     Rootstock Length, L                        Width, W   L + W Length of     Clone     (mm)     (mm)       (mm)  Petiole     ______________________________________     M9        101.7    63.8       165.5 32.5     (virus-free)     RN8       98.8     73.6       172.4 34.0     RN19      91.4     60.0       151.4 30.8     RN29      85.5     57.1       142.6 28.5     ______________________________________

3. The profuse blooming characteristic of RN8 is very pronounced and in this respect differs distinctly from its M9 parent. The number of blooms produced on RN8 two-year-old line-out stocks was about two-fold that of its M9 parent (Table 4).

                  TABLE 4     ______________________________________     Bloom Characteristics     (Research Station at Gorsum, Belgium - 1985)     Rootstock   % of Rootstocks With Bloom     Clone       (1 Year From Stoolbed)     ______________________________________     RN8         29     RN19        4     RN29        0     M9          15     (virus-free)     ______________________________________

4. Rooting ability (number and quantity of roots produced per length of stoolbed shank) of the subject clone is significantly more than that demonstrated strated by its M9 parent. Also, the average number of rooted plants produced per stoolbed mother plant and/or per meter of stoolbed row is significantly more than the average produced by M9 mother stocks (Table 5 , 6 and 7). This difference in number of rooted daughter plants was approximately two-fold at the test site near Bordeaux, France after five years in the stoolbed (Table 7). These characteristics are stable and have been transmitted without change through succeeding generations.

                  TABLE 5     ______________________________________     RN8 Stoolbed Production (Deveaux, Belgium)     No. Mother Plants - 555     Length of Bed (m) - 185     ______________________________________     Year       82/83   83/84   84/85 85/86  86/87     ______________________________________     Grade (mm)     10/12      300     150     150   1,100  500     8/10       0       0       700   0      0     6/10       4,650   3,350   0     0      2,800     6/8        0       0       3,700 3,100  0     5/7        0       0       0     0      0     4/6        2,400   1,800   3,200 1,900  3,900     04         0       600     0     0      0     #2s        1,000   1,400   600   900    1,900     Totals     8,350   7,300   8,350 7,000  9,100     Per Mother Plant                15.05   13.15   15.05 12.61  16.40     Per Meter  45.14   39.46   45.14 37.84  49.19     ______________________________________                                             Average     Year       87/88   88/89   89/90 90/91  82/91     ______________________________________     Grade (mm)     10/12      675     200     0     0     8/10       925     1,925   850   2,225     6/10       0       0       0     0     6/8        3,300   2,700   3,000 0     5/7        0       0       0     3,450     4/6        2,700   1,200   3,400 1,600     04         0       0       0     0     #2s        1,300   1,100   3,400 700     Totals     8,900   7,125   10,650                                      7,975     Per Mother Plant                16.04   12.84   19.19 14.37  14.96     Per Meter  48.11   38.51   57.57 43.11  44.89     ______________________________________

                  TABLE 6     ______________________________________     M9 (Virus-Free) Stoolbed Production (Deveaux, Belgium)     No. Mother Plants - 561     Length of Bed (m) - 187     ______________________________________     Year       82/83   83/84   84/85 85/86  86/87     ______________________________________     Grade (mm)     10/12      225     100     250   750    464     8/10       0       0       450   0      0     6/10       4,150   2,950   0     2,350  2,200     6/8        0       0       3,400 0      0     5/7        0       0       0     0      0     4/6        1,800   1,600   2,200 1,600  3,000     04         0       300     0     0      0     #2s        700     800     500   500    1,400     Totals     6,875   5,750   6,800 5,200  7,064     Per Mother Plant                12.25   10.25   12.12 9.27   12.59     Per Meter  36.76   30.75   36.36 27.81  37.78     ______________________________________                                             Average     Year       87/88   88/89   89/90 90/91  82/91     ______________________________________     Grade (mm)     10/12      75      --      --    --     8/10       450     --      --    --     6/10       0       --      --    --     6/8        2,700   --      --    --     5/7        0       --      --    --     4/6        2,200   --      --    --     04         0       --      --    --     #2s        400     --      --    --     Totals     5,825   --      --    --     Per Mother Plant                10.38   --      --    --     11.14     Per Meter  31.15   --      --    --     33.43     ______________________________________

                  TABLE 7     ______________________________________     Average Number of Plants Per Stoolbed Mother Plant     (Test Stooling Beds at Bordeaux, France)             Year Planted and Age     Rootstock 79/80    80/81  81/82  82/83     Clone     2-Yr     3-Yr   4-Yr   5-Yr Average     ______________________________________     M9        1.2      2.6    .5     4.0  8.3     (virus-free)     RN8       2.1      3.9    3.8    6.4  16.2     RN19      2.6      4.4    6.5    9.1  22.6     RN29      4.4      5.6    5.7    11.3 27.0     ______________________________________

BRIEF DESCRIPTION OF THE DRAWINGS

Since the subject clone is intended to be used only as rootstock for apple cultivar, the drawings center on the vegatative parts rather than the flowers and fruits.

FIGS. 1 and 2 show the absence of lateral brancess (feathers) on daughter stoolbed plants.

FIG. 3 shows the round- to oval-shaped leaves, broadly acute tips and sinuate leaf serration.

FIG. 4 shows the average height in centimeters of M9 rootstock daughter plants in a stoolbed row in Ephrata, Wash.

FIG. 5 shows the average height in centimeters of RN8 rootstock daughter plants in a stoolbed row in Ephrata Wash.

DESCRIPTION OF VEGATATIVE CHARACTERISTICS

The following is a detailed description of the new apple rootstocks growth characteristics based on the stoolbed plants grown at the six test sites described above. Colors of the leaves and shoots are based on their appearance at the sites where grown. In those instances where a precise color assessment can be made, reference is to the Munsell Limit Color Cascade Table. In other instances, general color terms are used in accordance with the ordinary dictionary significance.

General habit:

Strength of growth.--Vigorous, stiff.

Habit.--Upright.

Branching.--Very few, flexible.

Vegatative Shoots:

Bark color.--Greenish-brown (21-15).

Pubescence.--Very finely tomentose.

Lenticels.--Few, inconspicuous, widely spaced, small, white.

Leaves:

Size.--7.4 cm wide, 10.0 cm long.

Shape.--Oval to round, slightly asymmetric.

Base.--Obtuse, attenuated.

Apex.--Broadly acute.

Serrations.--Sinuate at sides, very obtuse to lacking at base.

Spacing.--Normal phyllotaxical arrangement for Malus.

Color.--Light green (22-14) with pinkish tips.

Leaf scars:

Shape.--Broad V, slightly raised.

Color.--Brown.

Petioles:

Shape.--Slender, slightly channeled.

Length.--Medium, 3.4 cm.

Color.--Reddish-brown (32-12).

Pose.--Acute angle near tip, slightly acute to horizontal along sides.

Glands.--None.

Stipules:

Size.--Small, 3.5-5 mm, inconspicuous, minutely serrated.

Color.--Light green.

Pose.--Mostly reposed along petiole.

Lateral buds:

Size.--Small.

Shape.--Flat, angular.

Color.--Dark brown.

Pubescence.--Finely tomentose.

Apical buds:

Size.--Larger than lateral buds.

Shape.--Obtuse.

Color.--Dark brown.

Pubescence.--Tomentose.

Dormant Plant

Shoots:

Size.--Stocky, 6-10 mm in caliper at base, stiff, brittle.

Bark Color.--Dark brown (25-15-l ).

Pubescence.--Conspicuously pubescent.

Nodes.--Larger in diameter than internodes with slight shoulder at each side on leaf scar.

Internodes.--Smooth, regularly spaced.

Stooling and Root Characteristics

Rooting and stooling: Multiplies well in stoolbeds, forming strong roots along full length of shank. Roots arise from nodes.

Habit of growth in stoolbed: Shoots arise from nodes, grow mostly outward at a slight angle.

Flower Characteristics

Flowers:

Size.--3.5 cm in diameter.

Color.--White with pink streaks at base.

Fruit:No commercial value, but useful for identification. No

Shape.--Round to slightly oblong.

Color.--Red Stripes.

Size.--About 4.5 cm in diameter and about 5.5 cm in length.

Flavor.--Bland, tasteless.

General Characteristics

Rootsuckering: Few rootsuckers.

Size control potential: Size of trees budded on the subject rootstocks will vary according to the vigor of the cultivar and/or type of soil and orchard management. "Standard" growing cultivars such as Red and Golden Delicious are reduced in size about 70% when compared to apple seedling rootstocks. Less vigorous varieties are more reduced in size and more vigorous varieties are less reduced in size.

Dwarfing: Fully dwarfing.

Precocity: Varies according to variety, most cultivars often flower and set fruit the first year in the orchard and thereafter bear fruit each year.

Compatibility: Graft compatible with all major commerical fruiting varieties.

Root Anchorage: Needs support.

Hardiness: Hardy in most commercial apple growing areas.

Disease and pest resistance: Average resistance to common diseases and pests of apple. Tested and found free of all known virus diseases to apple. 

What is claimed is:
 1. A new and distinct apple tree clone, a sport of the Malling 9, referred to by the cultivar designation `M9-RN8`, substantially as herein shown and described, characterized particularly by its ability to serve as a rootstock for grafting of apple tree cultivars to produce dwarf apple trees and by its ability to rot very readily in the stoolbed with very little lateral branching and produce high quality stoolbed rootstock plants for nursery use. 